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Author Topic: Glad |I asked first  (Read 4780 times)

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Re: Glad |I asked first
« Reply #30 on: February 09, 2018, 02:40:14 PM »
Backlash compensation can be useful for work where the forces from the cutting tool will
not cause the machine to move across the backlash zone, and where pauses of one
axis while another is compensating will not leave divots or burn marks.

Drilling a pattern of holes is an example where backlash compensation usually works
out OK. Pick and place operations for a robot is another that can benefit.

General purpose milling gets into trouble because climb cutting may cause the table
to move due to cutting forces and there is nothing the control software can due to
prevent that.
Steve Stallings
www.PMDX.com
For PMDX product support, please use PMDX forum or direct email for quickest response. We do not use this forum as our primary product support site.
Re: Glad |I asked first
« Reply #31 on: February 09, 2018, 03:37:56 PM »
Hi,
Steve has made a very nice summary of those situations where backlash compensation can be benefical.

For a mill with high cutting forces its not going to help.

Quote
.2" of backlash, INCHES? Tell me that's a typo!

No its no typo....and yes at 0.25 inch per turn, its almost a complete turn. The brass yoke is that worn the remaining threads must be so thin they break out some day soon.
While from time to time I do give this machine some hard work mostly it sits a month between jobs. I work repairing welding equipment and we might use it for facing
or otherwise shaping some insulation or shaping copper electrodes for a spotwelder for instance.

Despite the backlash you can still do some pretty good and accurate work with it but it takes patience and practice. Software cant do it, I can, and I prefer
to call myself 'squishyware'.

Craig

My wife left with my best friend...
     and I miss him!

Offline Chaoticone

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Re: Glad |I asked first
« Reply #32 on: February 09, 2018, 05:23:56 PM »
So basically what you guys are saying is that Mach 3/4's as well as the few controller that have implemented backlash compensation is all smoke and mirrors to get the customers to buy into their hype? Glad I learned something new.

If that is what you pulled out of it you need to pay more attention. Quit listening for what you want to hear and listen to what your being told.
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!
Re: Glad |I asked first
« Reply #33 on: February 09, 2018, 05:31:46 PM »
If that is what you pulled out of it you need to pay more attention. Quit listening for what you want to hear and listen to what your being told.

Or perhaps you need to get your message across in a way you mean it, which seems the below isn't:

The problem is the 99.9% of the cases it wont work in. Backlash compensation on a control truly is an oxymoron. And in those cases it wont work in, this is not just my opinion it's a simple fact. Until someone finds a bit of software that can rewrite the laws of physics the only fix for backlash is removing the mechanical backlash.

Offline RICH

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Re: Glad |I asked first
« Reply #34 on: February 09, 2018, 06:55:20 PM »
Quote
Or perhaps you need to get your message across in a way you mean it, which seems the below isn't:

Well after saying the same thing over, and over, and over, and over, all these years,  we sometimes try to change the way we reply so folks who can't get it get it. If at first we don't succeed we try, try again is our motto!  ;)

RICH
Re: Glad |I asked first
« Reply #35 on: February 10, 2018, 03:37:35 PM »
What does the quote button do on a post? Not a lot by the look of it. How do I quote a message?

Anyway BOT:

Quote Steve:  "General purpose milling gets into trouble because climb cutting may cause the table
to move due to cutting forces and there is nothing the control software can due to
prevent that."

Agreed there is no way backlash compensation can compensate when climb milling.

Answer: Don't climb mill on a hobby machine with backlash. This is standard newbee instruction.

However conventional milling should be more like lathe work where BLC is an every day "do it by hand" operation.

Sure BLC in a cnc controller would work very well on a lathe.

Re: Glad |I asked first
« Reply #36 on: February 10, 2018, 04:14:11 PM »
Hi Will,
you are correct....climb milling on ANY machine with significant backlash is a disaster waiting to happen.

What you are expecting of backlash compensation software is to replicate the same techniques that every competent machinist uses to achieve accurate
work in face of backlash. My experience is that computer software falls well behind an intelligent human operator....see my previous quip about 'squishyware'.

I think the way to proceed is to get a controller that has BLC and try it. I would caution you however that it MAY not be as good as you'd hoped and if that
proves to be the case you'll have to weather the 'I told you so'.

The quote button places two editing characters on your text input screen. Between these two characters you may paste a quote
previously saved to your clipboard.

Craig
My wife left with my best friend...
     and I miss him!
Re: Glad |I asked first
« Reply #37 on: February 11, 2018, 05:44:44 AM »
The quote button places two editing characters on your text input screen. Between these two characters you may paste a quote
previously saved to your clipboard.

Cheers Craig,

It didn't do that the other day though!!

Now it just quoted your whole message as I would expect - ah well at least something is working!

Offline RICH

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Re: Glad |I asked first
« Reply #38 on: February 11, 2018, 10:50:36 AM »
Quote
Sure BLC in a cnc controller would work very well on a lathe
.

Not really. If you want to do accurate work the heart of the machine, ball screws / bearings ,etc. must be as good as one can provide. Just as Brett has replied. I used BC on mills and lathes and it helped, BUT, the accuracy will never be consistant.Note  that every machine has some non-movement it's just a matter of degree. No one will ever convince me that BC will work just as good a mechanicaly correct machine.  

I do think that BC has a place to improve the preformance of many hobby machines. Many users are not going to spend the money for quality components or machines. That is fine, BUT,  they need to keep use of BC in perspective.

RICH

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Re: Glad |I asked first
« Reply #39 on: February 11, 2018, 12:18:39 PM »
Quote
The quote button places two editing characters on your text input screen. Between these two characters you may paste a quote
previously saved to your clipboard.

The quote button places two editing characters on your text input screen. Between these two characters you may paste a quote
previously saved to your clipboard.

Cheers Craig,

It didn't do that the other day though!!

Now it just quoted your whole message as I would expect - ah well at least something is working!

There are a couple of ways to insert quotes into post. They both work now and were the other day as well. Just below the search box there is a help button. It may help. Just because you don't know how something works doesn't mean it's broke.  ;)

Very true Rich.

Quote
No one will ever convince me that BC will work just as good a mechanically correct machine.

No and no one should waste their time trying to convince you or anyone else. It's simple physics and it doesn't take a rocket surgeon to understand it. They just need a little common sense and understanding of what backlash is.

Lots of controls backlash compensation works as good as is physically possible. But most often it will not be an acceptable solution. In the very few cases it will give acceptable results it could also be fixed with programming strategy.

So, in a nut shell, if you can write your programs to overcome the backlash of the machine and produce acceptable parts backlash comp. may be a feature you want to consider. Otherwise the only fix is to fix the backlash. It really is that simple. Anything else is a waste of your time and everyone's time that tries to help you.
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!